Andreas Finn

Biologically Inspired Omniphobic Surfaces by Reverse Imprint Lithography

Springtail skin morphology is translated into robust omniphobic polymer membranes by reverse imprint lithography. The combination of overhanging cross-sections and their arrangement in a self-supporting comblike pattern are crucial for mechanically stable coatings that can be even applied to curved surfaces.

In situ experiments to reveal the role of surface feature sidewalls in the Cassie-Wenzel transition.

Waterproof and self-cleaning surfaces continue to attract much attention as they can be instrumental in various different technologies. Such surfaces are typically rough, allowing liquids to contact only the outermost tops of their asperities, with air being entrapped underneath. The formed solid–liquid–air interface is metastable and, hence, can be forced into a completely wetted solid surface. A detailed understanding of the wetting barrier and the dynamics of this transition is critically important for the practical use of the related surfaces. Toward this aim, wetting transitions were studied in situ at a set of patterned perfluoropolyether dimethacrylate (PFPEdma) polymer surfaces exhibiting surface features with different types of sidewall profiles. PFPEdma is intrinsically hydrophobic and exhibits a refractive index very similar to water. Upon immersion of the patterned surfaces into water, incident light was differently scattered at the solid–liquid–air and solid–liquid interface, which allows for distinguishing between both wetting states by dark-field microscopy. The wetting transition observed with this methodology was found to be determined by the sidewall profiles of the patterned structures. Partial recovery of the wetting was demonstrated to be induced by abrupt and continuous pressure reductions. A theoretical model based on Laplace’s law was developed and applied, allowing for the analytical calculation of the transition barrier and the potential to revert the wetting upon pressure reduction.

Direct UV-Imprinting of Hybrid-Polymer Photonic Microring Resonators and Their Characterization

The direct patterning of hybrid-polymer microring resonators with minimal residual layers by UV-assisted nanoimprint lithography is reported. The proposed stamp-and-repeat technology requires no post-processing. The imprint polymer was applied by spin-coating as a 130-150 nm thin initial film for an optimized processing. The importance of the initial film thickness is discussed in detail. Aspect ratios of more than 5:1 were realized with 2 μm high ridge-waveguides and sub-400 nm coupling gaps on maximal 130 nm thin residual layers. The achieved ratio of structure height to residual layer thickness of 15.4 (2 μm versus 130 nm) was much larger than the typical values in high-resolution imprinting and superseded the removal of the residual layer completely. The resonators are thought as biosensor transducers. High quality devices with Q-factors up to 13000 were produced with a minimal set of process steps.

Biosensing with Optical Waveguides

The chapter gives an overview on modern technologies utilizing optical waveguides for biological, medical and environmental sensing. Section 28.2 presents state-of-the-art transduction mechanisms used in extrinsic sensor schemes as well as the potential and setup of the corresponding biooptrodes. The emphasis of Sect. 28.3 is on intrinsic methods, where the optical waveguide works as a bio-optical transducer itself. High precision techniques to evaluate the resulting changes of the waveguide’s properties will be discussed as well as the impact of the waveguide’s geometry on functionality and sensitivity of the sensor. In order to illustrate the variety of possible implementations, two novel biosensors will be presented in detail. The first one deploys a planar-optical waveguide to form a microring resonator, while the second uses grating structures inscribed in an optical fiber for the excitation of surface plasmon waves. Section 28.4 gives an introduction to the necessary biofunctionalization of the optical waveguide surface. Section 28.5 discusses the assembly of the sensor with focus on coupling and alignment of the light source.